Well, there's guys who like the bigger girls, but maybe not enough to justify the production of an anime that caters exclusively to em..

I think you pretty much answered why there isn't fat female leads . All you have to do is take a look at japanese culture , and there people . They have by far the lowest obese population in the world . Couple that with the fact that Japan most likely has more anime fans than the entire world (minus China) combined , and it is easy to see why we don't see them as leads .

Obese people and dragons are probably one in the same to most japanese people . Myths !

Pote Mayo from pote mayo !LOL
except shes more chubby then fat....wait i think i'm saying the same thing..........
anyways there's barely any fat main characters since in anime they want to make all the girls gorgus unless there's a joke to do with being ugly..........